A typical automotive radiator core is, structurally, a basic four-sided frame, with two parallel header plates and two parallel core reinforcements joined at their ends to the ends of the header plates. Both header plates and reinforcements are typically an aluminum alloy. Spaced aluminum tubes and interleaved corrugated air fins extend perpendicular to the header plates and parallel to the core reinforcements. The core reinforcement is typically channel shaped, with a wider bottom wall and two shorter side walls. The outer surface of the bottom wall engages the corrugation peaks of the outermost fins of the cores, and the shorter walls face outwardly. The reinforcements thus act to border the outermost air fins, protecting them against damage. When all parts have been assembled and stacked, bands are tightened around the reinforcements to hold the core together, which is then run through the braze oven. A layer of braze material on the surface of the various parts, generally at least the fins, header plates and core reinforcements, melts and is pulled by capillary action into the interfaces between parts, hardening later to rigidly fuse all parts together.
In operation in the vehicle, the core reinforcements can actually become a threat to the structural integrity of the core, without further processing. This is because the tubes expand with heating, especially a coolant first begins to flow, more readily than the reinforcements, which resist the core expansion and puts stress on the tube to header joints. A simple expedient that has been implemented to solve the problem has been to saw cut through each reinforcement, through both the side walls and bottom walls, after the core has been brazed. Post braze, the core is sufficiently rigid that the core reinforcements no longer are needed for structural integrity, and will still protect the outer fins, even if cut through. Once cut, the reinforcements no longer stress the joints with thermal expansion. However, the post braze cutting operation itself is expensive and difficult to control, creating potential for the tubes just under the reinforcement to be cut or damaged.
Consequently, a number of patents have disclosed methods to improve the post braze reinforcement cutting operation. U.S. Pat. No. 4,719,967 disclosed a core reinforcement which was pre sheared through the bottom wall and part of the side walls. In one embodiment, a thin, narrow cut is made, but it is recognized that the tendency of braze material to be drawn into crevices might cause a thin cut to be filled in and “repaired” in effect, during the braze operation. A second embodiment discloses a wider pre cut, too wide to be bridged and filled in. With such a pre cut, post braze, only part of the side walls remained to be sheared, avoiding the need for a deep and potentially tube damaging saw cut all the way down through the bottom wall. There have been many variations of this basic technique proposed since then. The post braze cutting operation is not eliminated, but is made simpler and less dangerous to the outer tubes.
Another approach proposed has been to extend the basic pre cut disclosed in U.S. Pat. No. 4,719,967 so far into the core reinforcements' side walls that only a narrow web of side wall material left would remain. The webs would be strong enough to keep the reinforcement whole during banding and brazing process, but weak enough, theoretically at least, to automatically break later, during operation of the radiator core, as the core expanded and the reinforcement was stressed. It would cut itself, in effect, eliminating the cost of the sawing or shearing operation. This basic concept was disclosed at least as early as the publication of Japanese application 1-131898 in 1989. A more recent patent, U.S. Pat. No. 6,328,098, claims to assist that automatic breaking process by pre bending or scoring the webs to further weaken them. Regardless, such a scheme relies on a level of expansion during radiator operation sufficient to break the reinforcement, and to do it fairly early in the operational life of the radiator. This is difficult to predict and control, and the header plate to tube joints will inevitably experience some stress before that occurs, unlike the standard methods of completely cutting the reinforcement before the radiator goes into operation.